Ok so this is probably a trivial question but I’m having trouble visualizing and understanding the differences and when to use each. I’m also a little unclear as to how concepts like uni-directional and bi-directional mappings affect the one-to-many/many-to-many relationships. I’m using Hibernate right now so any explanation that’s ORM related will be helpful. As … Read more
I’m defining my Django models right now and I realized that there wasn’t a OneToManyField in the model field types. I’m sure there’s a way to do this, so I’m not sure what I’m missing. I essentially have something like this: class Dude(models.Model): numbers = models.OneToManyField(‘PhoneNumber’) class PhoneNumber(models.Model): number = models.CharField() In this case, each … Read more
I think I misunderstood the meaning of cascading in the context of a @ManyToOne relationship. The case: public class User { @OneToMany(fetch = FetchType.EAGER) protected Set<Address> userAddresses; } public class Address { @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL) protected User addressOwner; } What is the meaning of the cascade = CascadeType.ALL? For example, if I … Read more
Hibernate throws this exception during SessionFactory creation: org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags This is my test case: Parent.java @Entity public Parent { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) private Long id; @OneToMany(mappedBy=”parent”, fetch=FetchType.EAGER) // @IndexColumn(name=”INDEX_COL”) if I had this the problem solve but I retrieve more children than I have, one child is null. private List<Child> children; } … Read more
